Starting device for autogenerators



Aug. 31, 1965 A. MOIROUX ETAL 4 STARTING DEVICE FOR AUTOGENERATORS Filed Feb. 1, 1965 IIInI'I'I'IuI'uI'II' INVEN TOR 1 5/1 ma/ziaux ATTURNEX;

United States Patent 4 Claims. (Cl. 60-14) This invention relates to a device for starting groups of free piston autogenerators interconnected by their reservoirs of compressed air.

The term free-piston autogenerators refers to machines or engines comprising a motor cylinder and at least one compressor cylinder and .wherein at least a great proportion of the air delivered by the compressor cylinder is fed to a reservoir of compressed air which communicates with the inlet ports of the motor cylinder, said air serving as scavenging and supply air for the motor cylinder to form, together with the incompletely expanded combustion gasses, a hot pressurised gaseous mixture which leaves the exhaust ports of the motor cylinder and is supplied as a driving gas to a prime mover, namely a turbine.

It has already been suggested that the reservoirs of compressed air of a number of free piston autogenerators should communicate with one another so that all the autogenerators together form an autogenerator group. If the group comprises two autogenerators, the same usually work in normal conditions in phase opposition i.e., when the free pistons of one autogenerator are at their dead centre positions, the free pistons of the other autogenerator are at their outer dead centre positions (offset of phase corresponding to 180). In other cases the autogenerators forming a group because of the interconnection between their reservoirs of compressed air operate in coincidence of phase.

Difiiculties may occasionally arise in the starting of an autogenerator group of this kind, since it is very difficult to start the autogenerators right away in the required phase relationship and in exactly the same conditions.

It is a main object of the invention to obviate these difliculties. The invention accordingly provides a process wherein at least the reservoirs of compressed air of the free piston autogenerators of a same group are separated during starting, the autogenerators being operated in this way for some time, especially during the warming-up time of said autogenerators, whereafter the connection between said reservoirs is made.

Moreover the invention provides, for performing said process, closure members in the communications between said reservoirs of the autogenerators of the same group and control means to actuate said closure members, said control means being adapted to hold these closure members closed for a while, especially in the starting period of the operation of said autogenerators.

For a better understanding of the invention and to show how the same may be carried into effect, reference may now be made to the accompanying drawings wherein:

FIG. 1 is a diagrammatic view showing a group comprising two free piston autogenerators working in phase opposition and supplying driving gases to a turbine, the group comprising the starting means according to the invention;

FIGS. 2, 3, and 4 are views, in section and under a enlarged scale, of the communicating passage which extends between the two autogenerators and which comprises closure means according to an alternative form of 3,203,164 Patented Aug. 31, 1965 "ice the invention and of exemplary means for controlling said closure members.

FIG. 5 is a section along V-V of FIG. 4.

The invention is shown applied to a group of two free piston autogenerators having substantially the same dimensions and whose reservoirs of compressed air are interconnected with one another, this group serving to supply driving gases to a turbine.

Except for some means for facilitating starting, the two free piston autogenerators A, B can be devised in any appropriate manner, for instance, in the manner shown in FIG. 1 wherein each autogenerator has a motor cylinder 1 operating preferably on the two-stroke diesel princlple-i.e., the fuel injected by an injector 2 is ignited by the heat of compression of the air compressed in the motor cylinder 1 during the inward stroke of a motor piston 3 working in the motor cylinder 1. The same is provided with at least one inlet port 4 and at least one exhaust port 5 controlled by the piston 3. A compressor piston 6 is rigidly connected to the piston 3, the two pistons 3, 6 forming a moving piston assembly, said compressor piston 6 operating in a compressor cylinder 7 rigidly connected to said motor cylinder 1.

In order to simplify the drawings, each of the autogenerators shown in FIG. 1 comprises only one piston assembly 3, 6. In practice, however, autogenerators usually comprise two opposed piston assemblies whose motor pistons 3 operate in opposed fashion in a single cylinder 1 and whose compressor pistons 6 operate in two cylinders 7 disposed on either side of the driving cylinder 1, the two opposed free pistons being interconnected conventionally by a synchronising system (not represented).

A casing 10 is disposed around the motor cylinder 1 and is adapted to receive the air compressed in said cylinder 7 by the inside face of the compressor piston 6 through inlet valves 9 provided in the partition between said casing 10 and said compressor cylinder 7. The interior space of said casing 7 is adapted to communicate with the interior space of the cylinder 1 when the piston 3 approaching its outer dead centre position uncovers the inlet port 4.

Inlet valves 8 are provided in the outer wall of cylinder 7 for the admission therein of air during this stroke outward of the piston assembly 3, 6.

The return or inward stroke of the moving piston assembly 3, 6 of each autogenerator A, Bi.e., the stroke during which the air trapped in the cylinder 1 is compressed to a temperature high enough to ignite the fuel injected by the injector 2 and during which the air inside the compressor cylinder 7 is compressed and delivered to the compressed air reservoir or casing 10 through said inlet valve 9is produced by a cushion of air trapped between the outside face of the piston 6 and the end 7a of the cylinder 7. The air cushion stores most of the energy developed in the motor cylinder 1 during the "outward stroke of the piston assembly 3, 6, then restores such energy thereto during its inward stroke.

For starting the machine shown in FIG. 1, the air is fed to the spaces containing the pneumatic cushions and which form the pneumatic energy accumulators, these cushions thus acting also as starting spaces, whereby the piston assembly 3, 6 is caused to move toward its inner dead centre position, to compress the air in the motor cylinder 1 and cause the combustion of the fuel injected at the termination of this inward stroke. The device controlling this introduction of starting air into each air cushion of the autogenerators A, B has the reference 11 in FIG. 1, and may be constituted by a tank containing air under high pressure which is released in the air cushions when the autogenerators are to be started through opening of a valve not represented.

The interior spaces of the reservoirs or casings 10 of two autogenerators A, B of a same group are interconnected by a duct 12. The exhaust ports too are interconnected by a duct 13; connected thereto is a duct 14 through which the hot pressurised mixture formed by the scavenging air and the combustion gases passes from each motor cylinder 1 to a turbine 15. If the two autogenerators thus interconnected are normally operated in phase oppositioni.e., with a 180 offset-a further device D must be provided between the air cushions for restoring the predetermined difference of phase, in the event of a disturbance thereof, such device D enabling the required transfers of air from the air cushion of the leading autogenerator to the air cushion of the lagging autogenerator. The device D can be of any appropriate kind, for instance, of the kind disclosed in the United States Patent No. 2,473,204 issued June 14, 1949.

It would be diflicult to start these two autogenerators with a predetermined difference of phase-Le, in phase oppositionsince a great accuracy is required at starting (the time offset between the startings of the individual autogenerators must not exceed 0.1 second and preferably should be less), and the starting conditions should be identical for both autogenerators. To obviate these difficulties, at least the casings of the two autogenerators are separated from one another in order for the latter to be started as ,two single machines. They are run singly for a while until each autogenerator has reached at least substantially its normal working temperature. Communication between the two casings or reservoirs 10 is then restored. The device D is also set out of operation during the starting period of operation of said autogenerators as long as they are separated.

According to the main feature of the invention, closure members are provided in the duct 12 interconnecting the two casings 10 of the two autogenerators, for interrupting the communication between the latter. For instance, the closure members cam take the form of a simple rotatable flap 16 which closes the duct 12 in one positionthe position shown in FIG. 1and thus separates the two casings 10 from one another, while in a position at right angles to the position shown in FIG. 1 the flap 16 opens the duct 12 to interconnect the casings 10.

In a variant of use, more particularly if the dimensions of the duct 12 are fairly large, several, for instance two flaps 16a, 16b may be used as shown in FIGS. 2 to 4; when in the horizontal position shown in FIG. 3, the flaps open the duct 12, and when in the vertical position shown in FIG. 2, they close the duct 12.

The closure means in the duct 12 can be controlled either directly by manual intervention or via a servomotor system which can be, for instance, hydraulic or pneumatic or electric. If required, this control can be automatic, in which event the automatic control system can operate in dependence upon a temperature characteristic of the heating of the autogenerator, for instance, the temperature of the air in the casings 10 or the temperature of the driving gases in the duct 12 or 14 or some other appropriate temperature or upon a pressure characteristic of the operation of said au'togenerator, for instance the average pressure in the casings 10 or the duct 12.

FIGS. 2 to 4 show exemplary embodiment of control systems for closure members such as described above. FIGS. 2 and 3 show the automatic control of the flaps 16a, 1612 by the temperature of the gases in the duct 12 connecting the respective casing 10 of the two autogenerators. The flaps 16a, 161) are actuated through a linkage system 18 which may be actuated by a magnetic coil 19. A thermometric element 20, known per se, transmits its dilatation to a lever arm 21 which coacts with an abutment 22 to form therewith a switch which holds an electric circuit 23, containing said magnetic coil 19, open for a temperature in the duct 12 equal or inferior to a predetermined value, corresponding to the normal operation of the group of autogenerators, said switch closing said circuit when the temperature in the duct 12 has not yet reached said predetermined value (during the starting period of the autogenerators). In addition, the linkage system 18 is permanently subjected to the force of a spring in a direction opposed to the force exerted on said linkage by said magnetic coil 19 when the electric circuit 23 is closed.

This system operate as follows: when starting the autogenerators the thermometric element 20 holds the electric circuit 23 closed and the magnetic coil overwhelms the counteracting force of the spring 24 as shown in FIG. 2, thereby holding the flaps 16a, 16b in their closed position. When the temperature of normal operation in the duct 12 is reached, the switch opens, the magnetic coil 19 is set out of operation and the spring 24 causes the linkage 18 to move the flaps 16a, 16b in the position shown in FIG. 3, thereby permitting the connectio between the casings 10 of the respective autogenerators of the group.

FIG. 4 shows an examplary embodiment of the control of said flaps 16a, 1612 by the average pressure for instance on one side of said flaps in the duct 12. The average pressure is transmitted to a cylinder 25 through a pipe 26 connected to said duct 12 through a throttle 27. This average pressure is delivered on the side 28a of a piston 28 which is subjected on its other face to the action of a spring 29, connected to the linkage 18, and which is adapted to yield when the average pressure acting on the side 28a of the piston reaches a predetermined value, for instance, that of normal operation of the group.

As long as the predetermined pressure for which said flap should be held open is not reached, the spring 29 holds the linkage 18 in the position for which the flaps 16a, 1622 close the duct 12.

On the contrary when the average pressure in the cylinder 25 goes beyond said predetermined value, it

overwhelms the spring 29 and causes the flaps to open (FIG. 5) whereby the interconnection between the respective casings 10 of the autogenerators of the group is realized.

In some other embodiments of the invention the opening of the closure members 16 may be operated automatically simply after a predetermined time following the starting of the autogenerators of the group.

As already stated, the invention is also of use in cases where the autogenerators forming the group work in coincidence of phase or with a difference of phase between zero and In particular when the autogenerators of the group work in coincidence of phase, a constant communication can be provided between the air cushions, as disclosed by the applicants United States Patent No. 2,912,964 issued November 17, 1959.

Clearly, and as the foregoing shows, the invention is not limited to that of its forms of application nor to those embodiments of its various parts which have been more particularly considered, but covers all the alternatives, modifications and equivalents as may be properly included within the spirit and scope of the invention as defined by the appended claims.

We claim:

1. In a group of autogenerators, each of which comprises a casing for compressed air, a motor cylinder in said casing, inlet ports in said motor cylinder adapted to connect the interior space thereof with the interior space of said casing, a motor piston reciprocating in said motor cylinder and uncovering said inlet ports when approaching one of its dead end centres thereby permitting the scavenging of said motor cylinder by the compressed air of said casing, a compressor cylinder connected with said motor cylinder, a compressor piston, integral with said motor piston, reciprocating in said compressor cylinder, means for feeding air in said compressor cylinder on the side of said compressor piston opposite to said motor piston for starting said autogenerator, at least one duct connecting the casings of said autogenerators, the provision of valve members in said duct and of means for holding said valve members in the position for which they shut the connections between the casings at least during the starting period of the operation of said autogenerators.

2. A group of autogenerators according to claim 1 wherein said means for holding said valve members in the position for which they shut the connections between the casing at least during the starting period of said autogenerator are responsive to the temperature of the compressed air in said casing.

3. A group of autogenerators according to claim 1 wherein said means for holding said valve members in the position for which they shut the connections between the casing at least during the starting period of said autogenerator are responsive to the pressure of the compressed air in said casing.

4. In a group of two autogenerators, each of which comprises a casing for compressed air, :a motor cylinder in said casing, inlet ports in said motor cylinder, adapted to connect the interior space thereof With the interior space of said casing, a motor piston reciprocating in said motor cylinder and uncovering said inlet ports when approaching one of its dead end centres thereby permitting the scavenging of said motor cylinder by the compressed air of said casing, a compressor cylinder connected with said motor cylinder, a compressor piston, integral with said motor piston, reciprocating in said compressor cylinder, means for feeding air in said compressor cylinder on the side of said compressor piston opposite to said motor piston for starting said autogenerator, a duct connecting the casings of said two autogenerators, the provision of valve members in said duct and of means for holding said valve members in the position for which they shut the connections between the casings at least during the starting period of the operation of said autogenerators.

No references cited.

JULIUS E. WEST, Primary Examiner. 

1. IN A GROUP OF AUTOGENERATORS, EACH OF WHICH COMPRISES A CASING FOR COMPRESSED AIR, A MOTOR CYLINDER IN SAID CASING, INLET PORTS IN SAID MOTOR CYLINDER ADAPTED TO CONNECT THE INTERIOR SPACE THEREOF WITH THE INTERIOR SPACE OF SAID CASING, A MOTOR PISTON RECIPROCATING IN SAID MOTOR CYLINDER AND UNCOVERING SAID INLET PORTS WHEN APPROACHING ONE OF ITS DEAD END CENTRIES THEREBY PERMITTING THE SCAVENGING OF SAID MOTOR CYLINDER BY THE COMPRESSED AIR OF SAID CASING, A COMPRESSOR CYLINDER CONNECTED WITH SAID MOTOR CYLINDER, A COMPRESSOR PISTON, INTEGRAL WITH SAID MOTOR PISTON, RECIPROCATING IN SAID COMPRESSOR CYLINDER, MEANS FOR FEEDING AIR IN SAID COMPRESSOR CYLINDER ON THE SIDE OF SAID COMPRESSOR PISTON OPPOSITE TO SAID MOTOR PISTON FOR STARTING SAID AUTOGENERATOR, AT LEAST ONE DUCT CONNECTING THE CASINGS OF SAID AUTOGENERATORS, THE PROVISION OF VALVE MEMBERS IN SAID DUCT AND OF MEANS FOR HOLDING SAID VALVE MEMBERS IN THE POSITION FOR WHICH THEY SHUT THE CONNECTIONS BETWEEN THE CASINGS AT LEAST DURING THE STARTING PERIOD OF THE OPERATION OF SAID AUTOGENERATORS. 